We wish to study the phosphorylation and dephosphorylation of various proteins of functionally different muscles in order to shed light on the molecular events of muscle contraction. Specific aspects of this program are: We will determine the incorporation of P32 into the following proteins: myosin (heavy and light chains), actin, tropomyosin, troponin components; and the following cellular fractions: sarcoplasm, myofibrils, mitochondria, and sarcoplasmic reticulum. The aim is to detect any specific phosphorylation of protein. Changes in the phosphate content of these proteins will be determined during a single isotonic or isometric tetanus of electrically stimulated frog muscle, electrical stimulation of the stretched muscle, and chemically induced contractures of the muscle. These experiments may reveal the role of protein phosphorylation in control of muscle function. We plan to study the effect of denervation, neuro transmitters, and various drugs on the turnover of protein-bound phosphorus in muscle. Several of the phosphoproteins will be subjected to proteolytic digestion and the composition of the radioactive peptides will be analyzed with the aim to determine the sequences of phosphorylation sites.